Integrated fuel processor for rapid start and operational control

ABSTRACT

A fuel processor for rapid start and operational control. The fuel processor includes a reformer, a shift reactor, and a preferential oxidation reactor for deriving hydrogen for use in creating electricity in a plurality of H 2 —O 2  fuel cells. A heating and cooling mechanism is coupled to at least the shift reactor for controlling the critical temperature operation of the shift reactor without the need for a separate cooling loop. This heating and cooling mechanism produces or removes thermal energy as a product of the temperature of the combustion of air and fuel. Anode effluent and cathode effluent or air are used to control the temperature output of the heating mechanism. A vaporizer is provided that heats the PrOx reactor to operating temperature.

FIELD OF THE INVENTION

[0001] The present invention generally relates to fuel processors and,more particularly, relates to a fuel processor having a two-stage leancombustion system for rapid start of the fuel processor and thermalintegration for reactor tempterature control.

BACKGROUND OF THE INVENTION

[0002] H₂—O₂ fuel cells use hydrogen (H₂) as a fuel and oxygen (as air)as an oxidant. The hydrogen used in the fuel cell can be derived fromthe reformation of a hydrocarbon fuel (e.g. methanol or gasoline). Forexample, in a steam reformation process, a hydrocarbon fuel (such asmethanol) and water (as steam) are ideally reacted in a catalyticreactor (a.k.a. “steam reformer”) to generate a reformate gas comprisingprimarily hydrogen and carbon monoxide.

[0003] An exemplary steam reformer is described in U.S. Pat. No.4,650,727 to Vanderborgh. For another example, in an autothermalreformation process, a hydrocarbon fuel (such as gasoline), air andsteam are ideally reacted in a combine partial oxidation and steamreforming catalytic reactor (a.k.a. autothermal reformer) to generate areformate gas containing hydrogen and carbon monoxide. An exemplaryautothermal reformer is described in U.S. application Ser. No.09/626,553 filed Jul. 27, 2000. The reformate exiting the reformercontains undesirably high concentrations of carbon monoxide most ofwhich must be removed to prevent poisoning of the catalyst of the fuelcell's anode. In this regard, carbon monoxide (i.e., about 3-10 mole %)contained in the H₂-rich reformate/effluent exiting the reformer must bereduced to very low nontoxic concentrations (i.e., less than about 20ppm) to avoid poisoning of the anode.

[0004] It is known that the carbon monoxide, CO, level of thereformate/effluent exiting a reformer can be reduced by utilizing aso-call “shift” reaction wherein water (i.e. steam) is added to thereformate/effluent exiting the reformer, in the presence of a suitablecatalyst. This lowers the carbon monoxide content of the reformateaccording to the following ideal shift reaction:

CO+H₂O→CO₂+H₂.

[0005] Some (i.e., about 0.5 mole % or more) CO still survives the shiftreaction. Hence, shift reactor effluent comprises hydrogen, carbondioxide, water carbon monoxide, and nitrogen.

[0006] The shift reaction is not enough to reduce the CO content of thereformate enough (i.e., to below about 20-200 ppm). Therefore, it isnecessary to further remove carbon monoxide from the hydrogen-richreformate stream exiting the shift reactor, and prior to supplying it tothe fuel cell. It is known to further reduce the CO content of H₂-richreformate exiting the shift reactor by a so-called “PrOx” (i.e.,preferential oxidation) reaction effected in a suitable PrOx reactoroperated at temperatures which promote the preferential oxidation of theCO with air in the presence of the H₂, but without consuming/oxidizingsubstantial quantities of the H₂ or triggering the so-called “reversewater gas shift” (RWGS) reaction. The PrOx and RWGS reactions are asfollows:

CO+½O₂→CO₂ (PrOx)

CO₂+H₂→H₂O+CO (RWGS)

[0007] The PrOx process is described in a paper entitled “Methanol FuelProcessing for Low Temperature Fuel Cells” published in the Program andAbstracts of the 1988 Fuel Cell Seminar, Oct. 23-26, 1988, Long Beach,Calif., and in Vanderborgh et al U.S. Pat. No. 5,271,916, inter alia.

[0008] Desirably, the O₂ required for the PrOx reaction will be abouttwo times the stoichiometric amount required to react the CO in thereformate. If the amount of O₂ exceeds about two times thestoichiometric amount needed, excessive consumption of H₂ results. Onthe other hand, if the amount of O₂ is substantially less than about twotimes the stoichiometric amount needed, insufficient CO oxidation mayoccur and there is greater potential for the RWGS reaction to occur.Accordingly in practice, many practitioners use about 4 or more timesthe stoichiometric amount of O₂ than is theoretically required to reactwith the CO.

[0009] PrOx reactors may be either (1) adiabatic (i.e. where thetemperature of the reactor is allowed to rise during oxidation of theCO) or (2) isothermal (i.e. where the temperature the reactor ismaintained substantially constant during oxidation of the CO). Theadiabatic PrOx process is sometimes effected via a number of sequentialstages, which progressively reduce the CO content in stages, andrequires careful temperature control, because if the temperature risestoo much, the RWGS reaction can occur which counter productivelyproduces more CO. The isothermal process can effect the same COreduction as the adiabatic process, but in fewer stages and withoutconcern for the RWGS reaction if (1) the reactor temperature can be keptlow enough, and (2) O₂ depletion near the end of the reactor can beavoided.

[0010] One known isothermal reactor is essentially a catalyzed heatexchanger having a thermally conductive barrier or wall that separatesthe heat exchanger into (1) a first channel through which the H₂-richgas to be decontaminated (i.e. CO removed) passes, and (2) a secondchannel through which a coolant flows to maintain the temperature of thereactor substantially constant within a defined working range. Thebarrier wall has a catalyzed first surface confronting the first channelfor promoting the CO+O₂ reaction and an uncatalyzed second surfaceconfronting the second channel for contacting the coolant therein toextract heat from the catalyzed first surface through the barrier. Thecatalyzed surfaces of adjacent barriers oppose each other, and areclosely spaced from each other, so as to define a narrow first channelthrough which the H₂-rich gas moves.

[0011] The reformation process of gasoline or other hydrocarbons operateat high temperatures (i.e. about 600-800° C.). The water gas shiftreactor is active at temperatures of 250-450° C., The PrOx reaction isactive at temperatures of 100-200° C. Thus, it is necessary that thereformer, the water gas shift (WGS) reactor, and the PrOx reactor areeach heated to temperatures sufficient for the fuel processor tooperate. During start-up, however, a conventional fuel processor is suchthat the heating of various components is staged. This approach can leadto undesirable lag time for bringing the system on line. Alternately,external electrical heat sources (i.e. heaters) may be employed to bringthe components to proper operating temperatures. This approach requiresan external source of electricity such as a battery.

[0012] Accordingly, there exists a need in the relevant art to provide afuel processor that is capable of heating the fuel processor componentsquickly to achieve these high operating temperatures for startup.Furthermore, there exists a need in the relevant art to provide a fuelprocessor that maximizes this heat input into the fuel processor whileminimizing the tendency to form carbon. Still further, there exists aneed in the relevant art to provide a fuel processor capable of heatingthe fuel processor while minimizing the use of electrical energy duringstartup and the reliance on catalytic reactions.

SUMMARY OF THE INVENTION

[0013] According to the principles of the present invention, a fuelprocessor for rapid start and operational control is provided having anadvantageous construction. The fuel processor includes a reformer, ashift reactor, and a preferential oxidation reactor for derivinghydrogen for use in creating electricity in a plurality of H₂—O₂ fuelcells. A heating or cooling mechanism, as required, is coupled to atleast the shift reactor for controlling the critical temperatureoperation of the shift reactor without the need for a separate coolingloop. This heating mechanism produces thermal energy as a product of thecombustion of air and fuel. Anode effluent and cathode effluent or airis used to control the temperature output of the heating mechanism.

[0014] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specificexamples, while indicating the preferred embodiments of the invention,are intended for purposes of illustration only and are not intended tolimit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

[0016]FIG. 1 is a schematic view illustrating a fuel processor accordingto a first embodiment of the present invention;

[0017]FIG. 2 is a schematic illustration of a combustion burner system;

[0018]FIG. 3 is a schematic view illustrating a fuel processor accordingto a second embodiment of the present invention; and

[0019]FIG. 4 is a schematic view illustrating a fuel processor accordingto a third embodiment of the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. For example, the present invention ishereafter described in the context of a fuel cell fueled by reformedgasoline. However, it is to be understood that the principles embodiedherein are equally applicable to fuel cells fueled by other reformablefuels.

[0021] Referring to FIG. 1, a fuel processor, generally indicated as 10,according to a first embodiment of the present invention is illustrated.Fuel processor 10 generally includes a first burner system 12, an autothermal reformer (reformer) 14, a heat exchanger 16, a water gas shiftreactor/heat exchanger (WGS/HX) 18, a preferential oxidation/vaporizer(PrOx/vaporizer) reactor 20, a fuel cell stack 22, a second burnersystem 24, and a catalytic combustor (comb) reactor 26.

[0022] First burner system 12 and second burner system 24 are primarilyused to heat the components of fuel processor 10 during a startup cycleto achieve rapidly and efficiently an optimal operational temperaturewithin fuel processor 10. First burner system 12 and second burnersystem 24 may burn various types of fuels, such as but not limited tohydrocarbons or hydrogen. Following such, fuel processor 10 is thencapable of efficiently producing electrical energy through thecombination of hydrogen and oxygen according to known fuel celltechnology. First burner system 12 and second burner system 24 are eachof either a premixed or diffusion-type burner that produces heat throughinternal combustion. The rate of heating is determined by the heatingvalue of the fuel that is burned. The amount of fuel burned is dependentupon the air stream rate at near overall stoichiometric conditions.First burner system 12 and second burner system 24 could be thermal orcatalytic in design.

[0023] Preferably, combustion heating occurs in two stages, namelywithin first burner system 12 and second burner system 24, to minimizethe initial temperature of the gases that are necessary to efficientlyand quickly heat reformer 14, WGS/HX 18, PrOx/vaporizer reactor 20, anda catalytic combustor 26 to operating temperature. That is, reformer 14,WGS/HX 18, PrOx/vaporizer reactor 20, and catalytic combustor 26 areeach susceptible to damage if exposed to excessive temperature. However,in order to heat these components to a predetermined operatingtemperature with a single burner, it is necessary that the output gasesof the single burner be sufficiently heated initially to carry enoughheat downstream to heat the remaining components. Therefore, the outputgases of the single burner may pose a risk to upstream components sincethe temperature may be above that which the upstream component iscapable of tolerating. Accordingly, it is preferable to employ a twostage heating system to effectively heat all components during start upwithout exposing such components to excessive temperature. Combustion intwo stages also serves to reduce the maximum flame temperature, whichreduces the production of undesirable NO_(x) formation. Alternatively,combustion could occur in more than two stages for improved localcontrol of the resultant heating. For example, an additional burnercould be used to heat WGS/HX 18 and PrOx/vaporizer reactor 20 directly.

[0024] As best seen in FIG. 1, fuel processor 10 is arranged such thatfirst burner system 12 includes a first air inlet stream 28 and a firstfuel inlet stream 30. First air inlet stream 28 may be obtained as adirect feed from a system air compressor (not shown) or from the airfeed 34 to fuel cell stack 22. The use of air from the air feed 34 tofuel cell stack 22 may provide additional flow rates to achieve higherheating capacity, if required.

[0025] The heated exhaust stream of first burner system 12, generallyindicated as 32, exits first burner system 12 as a fuel lean combustionexhaust to heat the downstream components of fuel processor 10. Theparticular temperature of first burner exhaust stream 32 is preferablysufficient to heat the catalyst within reformer 14 to its optimizedoperating temperature, typically in the range of about 600-800° C. forhydrocarbons, such as gasoline. To this end, first burner system 12 ispreferably a premixed or diffusion-type and includes a high temperaturezone for flame stability. It is contemplated that first burner exhauststream 32 of first burner system 12 may be diluted with downstream air(not shown) to control the first burner exhaust stream to a temperaturesuitable to heat the catalyst within reformer 14. This downstream airmay be obtained by diverting a portion of first air inlet stream 28within first burner system 12 or may be obtained by utilizing anotherair source (i.e. reformer air 36). However, first air inlet stream 28 ispreferably obtained as a direct feed from a compressor or fromtemporarily bypassing fuel cell stack 22 and using air supply from astack air inlet stream 34 to achieve a high flow rate of air. Thisarrangement, as illustrated in FIG. 1, minimizes the pressure dropthrough fuel processor 10 by preventing air from first air inlet stream28 from passing through heat exchanger 16 during startup and, further,by preventing a reformer air inlet stream 36 or a reformer steam 38 frompassing through first burner system 12 during normal operation.

[0026] Accordingly, first burner exhaust stream 32 from first burnersystem 12 sequentially heats a reformer inlet zone 40, reformer 14, heatexchanger 16, and a sulfur trap 42. A bypass valve 44 is opened and aWGS valve 46 is closed such that first burner exhaust stream 32 bypassesWGS/HX 18 and flows to catalytic combustor 26 and second burner system24. However, it should be understood that bypass valve 44 and WGS valve46 might be replaced with a single three-way valve (see FIG. 3).However, this two-valve arrangement enables bypass valve 44 to belocated away from the high temperature of reformate gas stream 54.Therefore, bypass valve 44 may be made of lower temperature, bettersealing materials to eliminate any leaks of reformate to catalyticcombustor 26, which may lead to a loss to system efficiency.

[0027] It is believed that a brief description of the remainingcomponents and connections of fuel processor 10 is beneficial toadequately describe the startup procedures and components. Hence, withreference to a “normal” operation (e.g. after the system has started upand is running), reformer inlet zone 40 includes a reformer fuel inletstream 48, such as gasoline, and reformer air and inlet flow 50 fromheat exchanger 16 to produce an inlet stream 52. Inlet stream 52 entersreformer 14 and catalytically reacts the fuel from reformer fuel inletstream 48 and air and water from reformer inlet flow 50 to form aH₂-rich reformate gas stream 54. Reformate gas stream 54 passes throughheat exchanger 16, which removes excess heat generated during thereformation cycle from reformate gas stream 54. This heat is then usedby heat exchanger 16 to heat a mixture of reformer air inlet stream 36and reformer steam 38 to produce reformer inlet flow 50. Reformate gasstream 54 then passes through sulfur trap 42 to remove sulfur and otherhydrocarbons and upon exit mixes with a water flow 56 to control thetemperature into WGS/HX 18 and further to humidify the effluent.

[0028] During normal operation, WGS valve 46 is open such that thehumidified reformate gas stream 54 passes therethrough to WGS/HX 18 andPrOx/vaporizer reactor 20. As mentioned above, WGS/HX 18 is a water gasshift reactor and heat exchanger combination system. The heat exchangerportion of WGS/HX 18 is fluidly separate from the water gas shiftreactor portion to enable efficient heating of the shift reactorcatalyst during the startup procedure.

[0029] PrOx/vaporizer reactor 20 is a preferential oxidation reactor anda vaporizer system. The vaporizer portion of PrOx/vaporizer reactor 20is used as a heat exchanger to remove excess heat from the preferentialoxidation reaction and to produce reformer steam 86 and separate thereaction catalysts from the steam flow. WGS/HX 18 and PrOx/vaporizerreactor 20 are used to reduce CO-level therein to acceptable levels. TheCO-depleted, H₂-rich reformate stream 58 is then fed into the anode sideof fuel cell stack 22. Simultaneously, oxygen from stack air inletstream 34 is fed into the cathode side of fuel cell stack 22. Thehydrogen from reformate stream 58 reacts with the oxygen from stack airinlet stream 34 across a membrane electrode assembly to produceelectricity. Anode exhaust or stack effluent 60 from the anode side offuel cell stack 22 includes a portion of hydrogen that is directed backto catalytic combustor 26 to provide heat. Cathode exhaust 62 from thecathode side of fuel cell stack 22 includes oxygen also for use incatalytic combustor 26. The flow of cathode exhaust 62 to catalyticcombustor 26 is controlled via a pair of control valves, namely acombustor air control valve 64 and a cathode exhaust back pressure valve66. The closing of cathode exhaust back pressure valve 66 produces aback pressure that forces air through combustor air control valve 64 forcombustion in catalytic combustor 26. The opening of cathode exhaustback pressure valve 66 permits flow to an exhaust 67.

[0030] During a startup cycle, bypass valve 44 is opened and WGS valve46 is closed, thereby sending the lean gases of first burner system 12indirectly to second burner system 24. It should be understood that itis necessary to bypass WGS/HX 18 when lean combustion gases are flowingwithin fuel processor 10, since the oxygen within the combustion gasesmay react with the CuZn catalyst that is typically used in water gasshift (WGS) reactors. However, if WGS/HX 18 includes a nonpyrophoriccatalyst, bypass valve 44 and WGS valve 46 are not necessary and leancombustion gases may be permitted to flow along the normal operationpath through fuel cell stack 22 to second burner system 24 to simplifyfuel processor 10. Generally, it is undesirable to allow dry air to flowthrough fuel cell stack 22 for extended periods of time due to thedrying of the membranes typically used in PEM stacks. However, accordingto the principles of the present invention, if valves 44, 46 were notused, the resultant gas flow through fuel cell stack 22 is acceptablesince it contains moisture, which is a product of the lean combustionwithin first burner system 12 and very low carbon monoxide levels toprevent “poisoning” of the catalysts. If desired, a bypass valve may beused to bypass fuel cell stack 22.

[0031] Second burner system 24 is used to indirectly heat catalyticcombustor 26, WGS/HX 18, and PrOx/vaporizer reactor 20. Second fuelinlet stream 68 is introduced downstream of catalytic combustor 26 andinto second burner system 24 such that during the combustion process,most of the remaining oxygen is consumed. However, it should be notedthat it is preferable to remain slightly fuel lean within second burnersystem 24 to insure that unburned hydrocarbons are not present in theheated exhaust stream 70. Second burner system 24 is preferably apremixed or diffusion-type. More preferably, second burner system 24 isa premixed type when used with liquid fuel to reduce the amount ofemissions produced by the flame.

[0032] As best seen in FIG. 2, catalytic combustor 26 is indirectlyheated. That is, under start conditions, combustor gas flow 88 to secondburner system 24 is the product of lean combustion in first burnersystem 12 flowing through bypass valve 44. Combustor gas flow 88 isindirectly heated across a liner 202, which separates a flame 204 ofsecond burner system 24 from combustor gas flow 88. Second fuel inletstream 68 is added to and mixes with combustor gas flow 88 aftercatalytic combustor 26. For premix operation, second fuel inlet stream68 is injected and mixes with the gas exiting the catalytic combustor 26in a mixing chamber 206 before introduction into flame chamber 208. Fordiffusion operation, there is no mixing in chamber 206 and second fuelinlet stream 68 is injected downstream of a flame holder 210 anddirectly into flame 204. For liquid fuel operation, the premixedapproach is preferred so as to reduce the amount of emissions from flame204. Flame holder 210 may be of any conventional type, such as but notlimited to a swirler, perforated plate (as shown in FIG. 2), backwardfacing step, bluff body, or transverse jets. Flame 204 can be initiatedby spark plug 212.

[0033] As best seen in FIGS. 1 and 2, a spray vaporization zone 72 isdownstream from second burner system 24, which employs a spray waterstream 74 to reduce the gas temperature of exhaust stream 70 exitingsecond burner system 24 in the event the exit temperature of exhauststream 70 is too high for a start vaporizer 80 or WGS/HX 18. Thetemperature of exhaust stream 70 exiting second burner system 24 isreduced as it passes through spray vaporization zone 72 and startvaporizer 80 to produce exhaust stream 82. Exhaust stream 82 then flowsthrough the heat exchanger of WGS/HX 18 and a run vaporizer 96 toexhaust 67.

[0034] Thermal energy from second burner system 24 is also utilized byinitiating a start vaporizer water stream 78 though start vaporizer 80to produce a start vaporizer steam flow 76. Start vaporizer steam flow76 flows across the backside of PrOx/vaporizer reactor 20 to heatPrOx/vaporizer reactor 20, since the saturation temperature of startvaporizer steam flow 76 (134° C. at 3 atm.) complements the operatingtemperature of the catalyst within PrOx/vaporizer reactor 20. It shouldbe appreciated that utilizing the heat of vaporization can transfersignificant thermal energy. Drains for eliminating condensed water maybe incorporated to avoid the use of thermal energy to revaporize thecondensed water. PrOx/vaporizer reactor 20 is of a heat exchanger typeconstruction to separate the reaction catalyst from start vaporizersteam flow 76, a PrOx inlet water flow 84, and the resulting PrOx steamflow 86 that is generated.

[0035] PrOx steam flow 86 provides additional heating of heat exchanger16, in addition to the direct heat provided to heat exchanger 16 byfirst burner system 12. If during the startup cycle the temperature of aWGS/HX exhaust exit flow 98 exceeds the vaporization temperature(typically about 150° C.), run vaporizer 96 can generate additionalsteam 102. That is, a run water 100 entering run vaporizer 96 isadjusted so that steam 102 is slightly superheated. Steam 102 joins withPrOx steam flow 86 to form reformer steam 38, which flows to heatexchanger 16. This process may be used to provide additional heating ofheat exchanger 16.

[0036] During a rapid start up cycle of fuel processor 10, full air flowis introduced in first air inlet stream 28 of first burner system 12.Bypass valve 44 is opened and WGS valve 46 is closed so as to route aflow 90 to second burner system 24. Ignition members 212, such as sparkplugs, within first burner system 12 and second burner system 24 areenergized. Simultaneously, first fuel inlet stream 30 and second fuelinlet stream 68 are introduced to first burner system 12 and secondburner system 24, respectively, to start combustion. Alternatesequencing may be appropriate depending on the mechanization hardware.Alternate scenarios could light off at reduced flow or lead with firstburner system 12 or second burner system 24. Confirmation of combustionwithin first burner system 12 and second burner system 24 is obtained bysensors such as flame ionization or temperature measurement of firstburner exhaust stream 32 and at the exit of spray vaporization zone 72,respectively. First fuel inlet stream 30 is controlled to produce thedesired temperature for the catalyst within reformer 14 (typically about600-800° C.) for gasoline type hydrocarbons.

[0037] Second fuel inlet stream 68 is controlled to maintain nearoverall stoichiometric conditions to maximize the heat input to fuelprocessor 10 for rapid startup. That is, the total fuel flow, whichequals the sum of first fuel inlet stream 30 and second fuel inletstream 68, reacts and consumes nearly all the oxygen provided by firstair inlet stream 28 to maximize the combustion heat produced withoutresulting in unburned hydrocarbons.

[0038] Spray water stream 74 is introduced within spray vaporizationzone 72 to maintain the proper temperature of exhaust stream 82 throughthe vaporization of water so as not to exceed the temperature limits ofthe downstream components. That is, spray water stream 74 ensures thatstart vaporizer 80, downstream from spray vaporization zone 72, is notexposed to excessively high temperatures (i.e. greater than about 600°C.). Moreover, spray water stream 74 ensures that exhaust stream 82 arenot excessively heated (typically less than about 300° C.) so as not todamage the CuZn type WGS catalyst. The control temperature may bealtered with the usage of precious metal based catalysts. A reduction ingas temperature further occurs across start vaporizer 80 due tovaporization of start vaporizer water stream 78. The quantity of startvaporizer water stream 78 is limited such that start vaporizer steamflow 76 is slightly superheated (typically about 150° C.). Furtherreduction in the quantity of start vaporizer water stream 78 is utilizedto favor heating WGS/HX 18 rather than PrOx/vaporizer reactor 20. Thestart operation is controlled as described above until fuel processor 10is heated to a predetermined temperature for normal operation.

[0039] Once the catalyst of PrOx/vaporizer reactor 20 and the catalystof WGS/HX 18 are above their minimum operation temperatures (typicallyabout 100° C. and about 220° C., respectively) and reformer steam 38 isflowing through heat exchanger 16, fuel processor 10 is ready to beginnormal operation. To determine whether such operating temperatures havebeen achieved, it is preferable to monitor and compare the temperatureof PrOx steam flow 86 to the operating temperature of PrOx/vaporizerreactor 20 and the temperature of WGS/HX exhaust exit flow 98 to theoperating temperature of WGS/HX 18. The availability of steam isdetermined by monitoring the temperature of reformer air and steam flow50. For high sulfur fuels, it is preferably that sulfur be removed fromthe liquid fuel or sulfur trap 42 be at its operating temperature(typically about 300-500° C.) to ensure full capacity such that sulfurdoes not pass to the catalyst of WGS/HX 18 or other downstreamcatalysts, as such catalyst may be damaged by the presence of sulfur.

[0040] Normal, fuel rich operation may be accomplished via severalmethods. For instance, fuel rich reformer flow for normal operation canbe established by starting reformer fuel inlet stream 48 and reformerair inlet stream 36, and closing first air inlet stream 28 and firstfuel inlet stream 30. Preferably, this transition occurs rapidly so asto not linger at near stoichiometric conditions due to the excessivelyhigh associated reaction temperatures. Moreover, this transition shouldpreferably occur quickly such that anatomic-oxygen-in-air-flow-to-carbon-in-fuel-flow ratio (oxygen-to-carbonratio) of less than one is not encountered, which may produceundesirable carbon.

[0041] Alternatively, normal, fuel rich operation may be established byinitially fully closing first fuel inlet stream 30 and first air inletstream 28 to first burner system 12. Reformer air inlet stream 36 andreformer fuel inlet stream 48 is then initiated in a way to preferablyavoid operation near stoichiometric conditions or oxygen-to-carbon ratioof less than one. However, operation in conditions where theoxygen-to-carbon ratio is less than one is permitted when steam flow isavailable. It is important to note that at least some steam flow isavailable after the start-up cycle from start vaporizer 80, runvaporizer 96, and PrOx/vaporizer reactor 20, which have all beenpreheated during the start-up cycle.

[0042] The change to fuel rich reformer operation is accompanied by theclosing of second fuel inlet stream 68 and the addition of cathodeexhaust 62 to catalytic combustor 26 to complete combustion beforeexhaust. To this end, catalytic combustor 26 must be kept sufficientlylean to maintain the catalyst temperature below its operating limit(typically about 750° C.). To this point, reformer fuel inlet stream 48is below its full power setting to insure that the operation ofcatalytic combustor 26 is within acceptable temperature limits (lessthan about 750° C.).

[0043] Once a stable flow through reformer 14 is established, WGS valve46 is opened and bypass valve 44 is closed to direct reformate gasstream 54 through the WGS portion of WGS/HX 18, the PrOx portion ofPrOx/vaporizer reactor 20, and fuel cell stack 22. In conjunction withthe changing of valve positions of bypass valve 44 and WGS valve 46, theflow of a PrOx air inlet stream 92 and PrOx inlet water flow 84 isinitiated into PrOx/vaporizer reactor 20. As fuel cell stack 22 drawscurrent, the hydrogen content of anode exhaust stream 60 is greatlyreduced, which reduced the reaction temperature within catalyticcombustor 26. Hence, spray water stream 74, if used, is controlled toproduce the desired temperature until it can eventually be shut off.Start vaporizer water stream 78 to start vaporizer 80 is also shut offand the control of the exit temperature of WGS/HX 18 is regulated usingcombustor air control valve 64, which controls the cathode exhauststream 62 to catalytic combustor 26.

[0044] If not initiated previously, run water 100 is initiated to runvaporizer 96 once the temperature of WGS/HX exhaust exit flow 98 exceedsthe water vaporization temperature (typically about 150° C.). Thequantity of run water 100 is determined within the energy availabilityof WGS/HX exhaust exit flow 98 to fully vaporize and the quantity ofwater available or desired for operation. Run vaporizer steam flow 102is available for reformer steam flow 38. Fuel processor 10 is now in anormal operating mode for producing electricity.

[0045] For normal operation, reformer air inlet stream 36 to reformerfuel inlet stream 48 ratio is set to provide the desired reformerreaction exit temperature (typically about 750° C.). The temperature ofreformate gas stream 54 into the front end of WGS/HX 18 (typically about250° C.) is controlled by the quantity of water flow 56 atomized intoand vaporized by reformate gas stream 54.

[0046] PrOx air inlet stream 92 is set to provide the required carbonmonoxide clean-up for fuel cell stack 22. Similarly, PrOx inlet waterflow 84 is set to remove the associated heat release from PrOx/vaporizerreactor 20. PrOx inlet water flow 84 is also set to provide single phasePrOx steam flow 86 as indicated by temperature measurements of thisstream. Alternate embodiments may adjust PrOx air and water flows toobtain optimum performance. For example, excess PrOx air may be used tohandle CO spikes, or two phase PrOx steam may be used to provide thermalbalance. Run vaporizer steam flow 102 is used as a surplus to increasethe fuel processor efficiency or to meet transient steam flowrequirements of the system, but is not utilized for thermal balance. Theincreased steam 102 provided by run vaporizer 96 also reduces the carbonmonoxide level from reformer 14, which helps to minimize the exothermwithin WGS/HX 18. Steam 102 from run vaporizer 96 can also be used tomoderate variations in reformer steam 38 or the molar steam flow toatomic carbon in fuel flow ratio (steam-to-carbon ratio). Furthercontrol of overall steam flow can be achieved through the use ofPrOx/vaporizer reactor 20. That is, if additional steam flow is requiredduring transient operation, PrOx air inlet stream 92 can be increased toprovide additional thermal energy by exothermic reaction with reformategas stream 104 within PrOx/vaporizer reactor 20 to vaporize additionalwater delivered to PrOx/vaporizer reactor 20 via PrOx inlet water flow84.

[0047] To increase or decrease the output from fuel processor 10,reformer fuel inlet stream 48 is increased or decreased, respectively,and the commensurate changes in air and water flows throughout thesystem are made to maintain the system thermal balance and stoichiometryas described above. The commensurate changes in air and water flows maylead or lag behind the changes in fuel flow to achieve the optimalresponse time and control within the desired reactor operating regimes.

[0048] It should be recognized that the present invention enables theunique capability to control the temperature of WGS/HX 18 and theability to handle unloads of fuel cell stack 22. The temperature ofreformate 54 before entering WGS/HX 18 is controlled using water flow56. Primary control of the temperature of WGS/HX 18 is provided byexhaust stream 82. The temperature of exhaust stream 82 can be adjustedby the amount of cathode exhaust 62 directed to catalytic combustor 26by combustor air control valve 64. According to the present embodiment,it is desirable that WGS/HX 18 operate at nearly constant temperatureand within the operating limits thereof. Preferably, as described above,CuZn catalyst is used within WGS/HX 18 wherein temperatures above about300° C. may damage the catalyst and temperatures below about 200° C.will greatly reduce the activity of the shift reaction. A challengeassociated with this narrow temperature window involves the removal ofheat generated by the exothermic reaction within WGS/HX 18, specificallyCO+H₂O→CO₂+H₂+thermal energy. By utilizing exhaust stream 82, which hasa relatively high mass flow rate and thus a high heat capacity ascompared to all of the available flow streams, the temperature rise(i.e. thermal energy) within WGS/HX 18 can be most effectivelyminimized. The ability to control the temperature of exhaust stream 82is also important to prevent quenching of the water gas shift reactionwith WGS/HX 18 (typically below about 220° C.), which may occur if thetemperature of exhaust stream 82 is too low. Indirect exothermicreduction is achieved by maximizing the quantity of reformer steam 38 toreformer 14, which lowers the carbon monoxide level entering WGS/HX 18.Maximizing the quantity of run water 100 vaporized in run vaporizer 96can also increase the flow of reformer steam 38. Still further,increasing the flow of PrOx air inlet stream 92 can increase the steamgenerating capacity of PrOx/vaporizer reactor 20. However, increasedflow of PrOx air inlet stream 92 may decrease the efficiency of fuelprocessor 10, which is not desirable for steady operation, but iseffective to increase steam generation during transient operations toavoid reducing the steam-to-carbon ratio or to limit the exotherm withinWGS/HX 18 to maintain the temperature of the WGS catalyst below damaginglevels.

[0049] At least three mechanisms are available for accommodating fuelcell stack 22 unloads. As used herein, the term unload refers to whenthe electric current draw from fuel cell stack 22 is reduced.Specifically, these mechanisms include 1) increasing cathode exhaust 62,2) initiating or increasing flow of start vaporizer water stream 78 tostart vaporizer 80, and 3) injecting spray water stream 74 into sprayvaporization zone 72. When fuel cell stack 22 unloads, the hydrogencontent of anode exhaust stream 60 increases. This increase in hydrogencontent will cause the temperature from catalytic combustor 26 toincrease. Since it is necessary to control the temperature of WGS/HX 18,it is necessary to limit or control the temperature of exhaust stream 70from catalytic combustor 26. Similarly, catalytic combustor 26 has anoperating temperature limit of typically about 750° C. Exceeding thisoperating temperature limit may damage the catalyst material withincombustor 26.

[0050] As a first measure, cathode exhaust 62 is controlled to cool thecatalyst of catalytic combustor 26 below its temperature limit. Thisenables exhaust stream 82 to be used to cool WGS/HX 18. If thetemperature of catalytic combustor 26 exceed the desired temperature ofWGS/HX 18 and all of the available cooling capacity of cathode exhaust62 is used, the temperature of exhaust stream 82 is lowered byinitiating or increasing flow of start vaporizer water stream 78 tostart vaporizer 80. This increases the steam-to-carbon ratio of fuelprocessor 10. Transition of water from run vaporizer 96 to startvaporizer 80 may be appropriate to dissipate excess heat in exhauststream 82, if excess water is not available. However, direct spray waterstream 74 may be used, particularly if the temperature into startvaporizer 80 exceeds its temperature limit (typically about 600° C.) orif an increased steam-to-carbon ratio in fuel processor 10 is notdesired. It is important to note that spray water stream 74 into exhauststream 70 is typically not recovered. Of course, as the load on fuelcell stack 22 decreases, the fuel flow and the overall fuel processoroutput is decreased to respond to the reduced power demand.

[0051] During a fuel processor shutdown, the electrical demand isreduced to a minimum predetermined level and fuel cell stack 22 isunloaded. When fuel cell stack 22 unloads, the H₂ content of anodeexhaust stream 60 increases and, thus, increased flow of cathode exhaust62 through combustor air control valve 64 is required to limit thecatalyst temperature of catalytic combustor 26. Bypass valve 44 is thenopened and WGS valve 46 is closed to direct the reformate gas streamthrough bypass valve 44 to catalytic combustor 26. PrOx air inlet stream92 and PrOx inlet water flow 84 are also shut off. Still further, runwater 100, reformer air inlet stream 36, and reformer fuel inlet stream48 are shut off. If desired, continuing the flow of cathode exhaust 62over the backside (or HX) of WGS/HX 18 can cool WGS/HX 18. Thiscontinued flow may be desirable to reduce the temperature of thecatalyst within WGS/HX 18 to lower its catalytic activity in the eventit becomes exposed to air leaks after shutdown. However, WGS valve 46and check valves (such as in anode exhaust 60) provide protectionagainst air leaking into WGS/HX 18.

[0052] As best seen in FIGS. 3 and 4, alternative embodiments of thepresent invention are illustrated, generally indicated as 10′ and 10″,respectively. It should be noted that like reference numerals designatelike or corresponding parts throughout the several views.

[0053] Referring in particular to FIG. 3, reformer air inlet stream 36of fuel processor 10′ is used to serve first burner system 12. Thisarrangement may require a substantially larger flow control range forreformer air inlet stream 36. However, if a single reformer air inletstream 36 is used with a single heat exchangers (such as heat exchanger16 illustrated in FIG. 1), the inlet air and steam (such as reformer airand steam flow 50) includes both air and steam, which may potentiallyextinguish the flame within first burner system 12 during a startupcycle. Therefore, as seen in FIG. 3, three heat exchangers 302, 304, and306 may be used to provide a dry combustion air to first burner system12.

[0054] According to this embodiment, reformer air inlet stream 36 andreformer steam inlet stream 38 are heated separately. The separate steamline then enters downstream from first burner system 12, as shown inFIG. 3, to reduce pressure drop and minimize the potential for flameextinguishing in first burner system 12.

[0055] Still referring to FIG. 3, run vaporizer 96 may be eliminated andstart vaporizer 80 may be used for producing the required steam output,thereby reducing the number of necessary components. However, it shouldbe understood that the amount of steam through steam flow 76 might bereduced as a result of the need to regulate the temperature of exhauststream 82 to WGS/HX 18.

[0056] Referring now to FIG. 4, an alternative arrangement isillustrated using a single vaporizer 402 is used to replace startvaporizer 80 and run vaporizer 96. However, as seen in FIG. 4, the flowdirection through vaporizer 402 is reversible so as to function upstreamof WGS/HX 18 during startup and downstream of WGS/HX 18 after startup.This requires the addition of an on/off exhaust valve 404 to redirectexhaust flow 406. According to this embodiment during startup, athree-way bypass valve 408 is actuated such that flow is directedthrough bypass line 410. Exhaust valve 404 is closed to prevent the flowthrough bypass line 410 from going to exhaust 67, thereby directing theflow to second burner system 24. Combustor air control valve 64 andexhaust backpressure valve 66 are each opened to allow the exhaust flowout to exhaust 67.

[0057] Hence, the flow path during a startup cycle is from first burnersystem 12, through reformer 14, heat exchanger 16, sulfur trap 42,through bypass valve 408 to bypass line 410, and then to second burnersystem 24. From second burner system 24, exhaust gases flow throughspray vaporization zone 72, vaporizer 402, WGS/HX 18, and catalyticcombustor 26. After catalytic combustor 26, exhaust gases flowingthrough line 412 are routed to exhaust 67 through open valves 64 and 66.The control of first burner system 12 and second burner system 24, inaddition to the water flows, is control as described above with relationto the system illustrated in FIG. 1.

[0058] For transition to normal operation, the present embodimentrequires that valving be changed before transitioning reformer 14 tofuel rich operation. That is, when fuel processor 10″ has been heated tooperating temperature, first fuel inlet stream 30 and second fuel inletstream 68 are stopped and first air inlet stream 28 is closed. Reformersteam 38 from vaporizer 402 may continue to purge reformer 14, heatexchanger 16, and sulfur trap 42 of air before initiating flow intoWGS/HX 18. Bypass valve 408 is then actuated to direct flow through line414 to WGS/HX 18 and PrOx/vaporizer reactor 20.

[0059] Air flow to catalytic combustor 26 is established through itsnormal flow path by starting stack inlet air stream 34 through fuel cellstack 22, cathode exhaust 62, combustor air control valve 64 (with backpressure from the closure of exhaust back pressure valve 66), and line412. Exhaust valve 404 is then opened to permit flow from exhaust stream70 to exhaust 67. Fuel rich flow into reformer 14 is then initiated bystarting reformer fuel inlet stream 48, reformer air inlet stream 36,PrOx air inlet stream 92, and PrOx inlet water flow 84. Timing of fuelinlet stream 48, air inlet stream 36, PrOx air stream 92, PrOx waterstream 84, and vaporizer water stream 78 may have offsets with relationsto each other dependent on the physical hardware utilized. Fuelprocessor 10″ is now in normal operation mode. With this arrangement,unload of fuel cell stack 22 is handled by increasing the flow rate ofcathode exhaust 62 through combustor air control valve 64.

[0060] According to the principles of the present invention, a fuelprocessor is provided that is capable of heating the fuel processorcomponents quickly to achieve proper operating temperatures for startup.Furthermore, the fuel processor of the present invention maximizes thisheat input into the fuel processor while minimizing the tendency to formcarbon. Still further, the fuel processor of the present inventionprovides a fuel processor capable of heating the fuel processorcomponents while minimizing the use of electrical energy during startupand the reliance on catalytic reactions. It should be readilyappreciated by those skilled in the art that the present inventionenables the potential usage of inexpensive CuZn catalyst only withoutthe need for an additional coolant loop. Moreover, the tight control oftemperatures within the fuel processor, which is afforded by the presentinvention, enables the optimization of reactor size and catalyst usageresulting in reduced active metal costs. Still further, the presentinvention provides improved transient carbon monoxide concentrationperformance.

[0061] The description of the invention is merely exemplary in natureand, thus, variations are not to be regarded as a departure from thespirit and scope of the invention.

What is claimed is:
 1. A reforming fuel cell system comprising: areformer converting a hydrogen-containing fuel to produce anH₂containing reformate having a level of carbon monoxide; a firstreactor operable to reduce said level of carbon monoxide of saidreformate; a fuel cell stack generating electrical energy from saidreformate and discharging an H₂-containing anode effluent and anO₂-containing cathode effluent; a combustor having a catalyst beddisposed therein for burning said anode effluent to generate an exhaustgas; a heat exchanger thermally coupled to said first reactor to controlthe temperature thereof, said heat exchanger having an input fluidlycoupled to said combustor to receive said exhaust gas; and a controlleroperable for metering air flow to said combustor to control thecombustion temperature thereof;
 2. The fuel processor according to claim1 wherein said controller comprises: a cathode control valve systemdisposed between said fuel cell stack and said combustor, said cathodecontrol valve system operable to direct said cathode effluent to saidcombustor to control the temperature of said combustor as a function ofthe H₂ content of said anode effluent.
 3. The fuel processor accordingto claim 2 wherein said cathode control valve system comprises: a firstcontrol valve fluidly coupled between said fuel cell stack and saidcombustor, said first control valve selectively actuated between anopened position to enable flow of said cathode effluent to saidcombustor and a closed position to prevent flow of said cathode effluentto said combustor; and a second control valve fluidly coupled betweensaid fuel cell stack and an exhaust passage, said second control valveselectively actuated between an opened position to enable exhausting ofsaid cathode effluent and a closed position to provide a back pressureto facilitate flow of said cathode effluent through said first controlvalve.
 4. The fuel processor according to claim 1, further comprising: asecond reactor disposed between said first reactor and said fuel cellstack, said second reactor being operable to further reduce carbonmonoxide levels of said reformate exiting said first reactor; acombustion heater outputting a heated exhaust stream; and a startvaporizer disposed downstream from said combustion heater, said startvaporizer being exposed to said heated exhaust stream for vaporizing aninlet fluid to produce a steam, said steam from said start vaporizerbeing directed to a heat exchanger element associated with said secondreactor for heating said second reactor.
 5. The fuel processor accordingto claim 4, further comprising: a spray vaporizer selectively injectinga cooling fluid into said heated exhaust stream to reduce the fluidtemperature thereof.
 6. The fuel processor according to claim 4, furthercomprising: a run vaporizer exposed to an exhaust flow from a heatexchanger element of said first reactor for vaporizing an inlet fluid toproduce a steam, said steam from said run vaporizer being directed to aninlet of said reformer.
 7. The fuel processor according to claim 1,further comprising: a second reactor disposed between said first reactorand said fuel cell stack, said second reactor being operable to furtherreduce carbon monoxide levels of said reformate exiting said firstreactor; a combustion heater outputting a heated exhaust stream; a sprayvaporizer selectively injecting a cooling fluid into said heated exhauststream to control the fluid temperature thereof; and a start vaporizerfluidly coupled to said combustion heater, said start vaporizer beingexposed to said heated exhaust stream for vaporizing an inlet fluid toproduce a steam stream, said steam stream being directed to a heatexchanger element of said second reactor for heating said secondreactor; wherein a flow through said combustion heater, said sprayvaporizer, said start vaporizer, said first reactor, and said combustoris reversible so as to alternatively position said combustion heater,said spray vaporizer, and said start vaporizer upstream and downstreamfrom said first reactor.
 8. A fuel processor for rapid start andoperational control, said fuel processor comprising: a plurality of fuelcells discharging an H₂-containing anode effluent and an O₂-containingcathode effluent; a reformer converting a hydrogen-containing fuelselected from the group consisting of alcohol and hydrocarbons to H₂ toproduce a reformate for fueling said plurality of fuel cells; a shiftreactor disposed between said plurality of fuel cells and said reformer,said shift reactor having a catalytic region operable to reduce carbonmonoxide levels of said reformate and a heat exchange region; apreferential oxidation reactor disposed between said shift reactor andsaid plurality of fuel cells, said preferential oxidation reactor beingoperable to further reduce carbon monoxide levels of said reformateexiting said shift reactor; a combustor providing hot exhaust gas tosaid heat exchange region of said shift reactor, said combustor having acatalyst bed disposed therein for burning said anode effluent and saidcathode effluent to generate said hot exhaust gas; a combustion burneroperably coupled to said combustor, said combustion burner outputting aheated exhaust stream; and a cathode control valve system disposedbetween said plurality of fuel cells and said combustor, said cathodecontrol valve system operable to direct said cathode effluent to saidcombustor to control a temperature of said combustor when the H₂ contentof said anode effluent increases.
 9. The fuel processor according toclaim 8 wherein said cathode control valve system comprises: a firstcontrol valve fluidly coupled between said plurality of fuel cells andsaid combustor, said first control valve selectively actuated between anopened position to enable flow of said cathode effluent to saidcombustor and a closed position to prevent flow of said cathode effluentto said combustor; and a second control valve fluidly coupled betweensaid plurality of fuel cells and an exhaust passage, said second controlvalve selectively actuated between an opened position to enableexhausting of said cathode effluent and a closed position to provide aback pressure to facilitate flow of said cathode effluent through saidfirst control valve.
 10. The fuel processor according to claim 9,further comprising: a spray vaporizer selectively injecting a coolingfluid into said heated exhaust stream to reduce the fluid temperaturethereof; and a start vaporizer disposed downstream from said combustionburner, said start vaporizer being exposed to said heated exhaust streamfor vaporizing an inlet fluid to produce a steam, said steam from saidstart vaporizer being directed to a heat exchanger element associatedwith said preferential oxidation reactor for heating said preferentialoxidation reactor.
 11. The fuel processor according to claim 10, furthercomprising: a run vaporizer exposed to an exhaust flow of said heatexchanger region of said shift reactor for vaporizing an inlet fluid toproduce a steam, said steam from said run vaporizer being directed to aninlet of said reformer.
 12. The fuel processor according to claim 8,further comprising: a spray vaporizer selectively injecting a coolingfluid into said heated exhaust stream to control the fluid temperaturethereof; and a start vaporizer fluidly coupled to said combustionburner, said start vaporizer being exposed to said heated exhaust streamfor vaporizing an inlet fluid to produce a steam stream, said steamstream from said start vaporizer being directed to a heat exchangerelement of said preferential oxidation reactor for heating saidpreferential oxidation reactor; wherein a flow through said combustionburner, said spray vaporizer, said start vaporizer, said shift reactor,and said combustor is reversible so as to alternatively position saidcombustion burner, said spray vaporizer, and said start vaporizerupstream and downstream from said shift reactor.
 13. A fuel processorfor rapid start and operational control, said fuel processor comprising:a plurality of fuel cells discharging an H₂-containing anode effluentand an O₂-containing cathode effluent; a reformer converting ahydrogen-containing fuel selected from the group consisting of alcoholand hydrocarbons to H₂ to produce a reformate for fueling said pluralityof fuel cells; a shift reactor disposed between said plurality of fuelcells and said reformer, said shift reactor being operable to reducecarbon monoxide levels of said reformate; a preferential oxidationreactor disposed between said shift reactor and said plurality of fuelcells, said preferential oxidation reactor being operable to furtherreduce carbon monoxide levels of said reformate exiting said shiftreactor; a combustor providing hot exhaust gas to said shift reactor,said combustor being fueled by said fuel and said anode effluent, saidcombustor having a catalyst bed disposed therein for burning said fueland said anode effluent to generate said hot exhaust gas; a combustionburner operably coupled to said combustor, said combustion burneroutputting a heated exhaust stream; a spray vaporizer selectivelyinjecting a cooling fluid into said heated exhaust stream to reduce thefluid temperature thereof; and a controller operable for metering airflow to said combustor to control the combustion temperature of saidcombustor.
 14. The fuel processor according to claim 13, furthercomprising: a cathode control valve system disposed between saidplurality of fuel cells and said combustor, said cathode control valvesystem operable to direct said cathode effluent to said combustor tolimit a temperature of said combustor when the H₂ content of said anodeeffluent increases.
 15. The fuel processor according to claim 14 whereinsaid cathode control valve system comprises: a first control valvefluidly coupled between said plurality of fuel cells and said combustor,said first control valve selectively actuated between an opened positionto enable flow of said cathode effluent to said combustor and a closedposition to prevent flow of said cathode effluent to said combustor; anda second control valve fluidly coupled between said plurality of fuelcells and an exhaust passage, said second control valve selectivelyactuated between an opened position to enable exhausting of said cathodeeffluent and a closed position to provide a back pressure to facilitateflow of said cathode effluent through said first control valve.
 16. Thefuel processor according to claim 13, further comprising: a startvaporizer disposed downstream from said combustion burner, said startvaporizer being exposed to said heated exhaust stream for vaporizing aninlet fluid to produce a steam, said steam from said start vaporizerbeing directed to a heat exchanger element associated with saidpreferential oxidation reactor for heating said preferential oxidationreactor.
 17. The fuel processor according to claim 16, furthercomprising: a run vaporizer exposed to an exhaust flow from a heatexchanger element of said shift reactor for vaporizing an inlet fluid toproduce a steam, said steam from said run vaporizer being directed to aninlet of said reformer.
 18. The fuel processor according to claim 13,further comprising: a start vaporizer fluidly coupled to said combustionburner, said start vaporizer being exposed to said heated exhaust streamfor vaporizing an inlet fluid to produce a steam stream, said steamstream from said start vaporizer being directed to a heat exchangerelement of said preferential oxidation reactor for heating saidpreferential oxidation reactor; wherein a flow through said combustionburner, said spray vaporizer, said start vaporizer, said shift reactor,and said combustor is reversible so as to alternatively position saidcombustion burner, said spray vaporizer, and said start vaporizerupstream and downstream from said shift reactor.
 19. A method forcontrolling a reforming fuel cell system, the method comprising thesteps of: generating a H₂-containing reformate in a reformer, saidreformate having a level of carbon monoxide; passing said reformatethrough a first reactor to reduce said level of carbon monoxide in saidreformate; reacting said reformate with oxygen in a fuel cell stack tocreate electrical energy and an anode effluent; inputting said anodeeffluent into a combustor to generate a exhaust stream; adjustablyinputting an oxidant into said combustor to control the temperature ofsaid exhaust stream; and transferring heat from said exhaust stream tosaid first reactor such that the temperature of said first reactor ismaintained within an operating range.
 20. The method of claim 19 whereinthe heat generated in said first reactor is balanced with the heattransferred to said first reactor from said exhaust stream to maintainsaid the temperature of said first reactor within said operating range.21. The method of claim 19 wherein the step of adjustably inputting anoxidant into said combustor is based on the temperature of said firstreactor.
 22. The method of claim 19 wherein said fuel cell stack createsa cathode effluent which is adjustably input into said combustor as saidoxidant.
 23. The method of claim 19 further comprising the step ofcontrolling the temperature of said exhaust stream by extracting heatfrom said exhaust stream prior to transferring said heat to said firstreactor.
 24. The method of claim 23 wherein the step of extracting heatfrom said exhaust stream comprises introducing a cooling spray streaminto said exhaust stream.
 25. The method of claim 24 further comprisingthe step of adjusting the rate of said cooling spray stream as afunction of the amount of said anode effluent produced.
 26. The methodof claim 23 wherein the step of extracting heat from said exhaust streamcomprises passing said exhaust stream through a vaporizor to produce asteam stream.
 27. The method of claim 26 further comprising the step ofinputting said steam stream through a second reactor disposed betweensaid first reactor and said fuel cell stack.
 28. The method of claim 27further comprising the step of adjusting a rate of steam stream throughsaid second reactor such that the temperature of said second reactor ismaintained within a second operating range.
 29. In a fuel processingsystem of the type having a reformer breaking down a hydrocarbon fuelinto an H₂ containing reformate stream and first and second rectorsdisposed downstream of the reformer for reducing the level of carbonmonoxide in the reformate stream, a method of rapidly starting the fuelprocessing system: generating a heated gas stream in a heating device;directing said heated gas stream through a first side of a heatexchanger; directing water through a second side of said heat exchangerto produce a steam stream; heating said first reactor with said heatedgas stream at a first rate of heating; heating said second reactor withsaid steam stream at a second rate of heating; and controlling saidheating device to adjust said heated gas stream, thereby controllingsaid first and second rates of heating.
 30. The method of rapidlystarting a fuel processing system of claim 29, further comprising thestep of injecting water into said heated gas stream to control thetemperature of said heated gas stream. 31 The method of rapidly startinga fuel processing system of claim 29, further comprising adjusting saidheating device as a function of the temperature of at least one of saidfirst and second reactors. 32 The method of rapidly starting a fuelprocessing system of claim 29, further comprising the step of generatinga second heated gas stream in a second heating device and directing saidsecond heated gas stream through said reformer to heat said firstreactor at a third rate of heating.
 33. The method of rapidly starting afuel processing system of claim 32, further comprising the step ofheating said reformer with said steam stream.
 34. The method of rapidlystarting a fuel processing system of claim 33, further comprising thesteps of directing said reformate stream through a first side of asecond heat exchanger and directing said steam stream through a secondside of said second heat exchanger.